1. Field of the Invention
The present invention relates to an intake device provided in an internal combustion engine and more particularly to a waterproof construction provided in an intake device which is provided with a negative pressure outlet port for taking out negative pressure generated in an intake passage for preventing water from entering into the negative pressure outlet port.
2. Description of Related Art
In an intake device of an internal combustion engine, sometimes moisture which is present in air flowing through an intake passage formed by passage walls adheres to inner surfaces of the passage walls in the form of water drops. In this case, the water drops may flow along the inner surfaces to enter into a negative pressure passage from a negative pressure outlet port which opens to the intake passage and become frozen due to a reduction in atmospheric temperature when the internal combustion engine is stopped. Thus, a negative pressure is prevented from taking-out from the negative pressure outlet port immediately after the internal combustion engine is started to operate. To address these problems, there are known various waterproof constructions for suppressing the entering of water drops into the negative pressure outlet port. For example, refer to Japanese Unexamined Patent Publications JP-A-2007-40142 and JP-A-2004-124831.
In a waterproof construction in which inner surfaces of passage walls which form an intake passage extend in a vertical direction and a negative pressure outlet port opens to a projecting portion which is provided on the inner surface so as to project into the intake passage, water drops which flow downwards along the inner surface is guided so as not to reach the negative pressure outlet port by a rising surface of the projecting portion. However, since the projecting portion which projects into the intake passage hinders the flow of intake air, the passage resistance of the intake passage is increased and intake efficiency is lowered.
In addition, in a waterproof construction in which a recessed portion is provided on an inner surface of passage walls, although the increase in passage resistance of the intake passage is suppressed compared with the waterproof construction in which the projecting portion is provided, a projecting portion (for example, a baffle plate) which projects towards an opening formed in the recessed portion so as to prevent the entering of water drops into a negative pressure outlet port needs to be provided within the recessed portion so as to surround the negative pressure outlet port. Accordingly, the recessed portion is enlarged and the disposition of the negative pressure outlet port in the intake device becomes restricted. In addition, the construction of the recessed portion becomes complex and the production costs of the intake device increases.
In addition, in the passage wall, because the projecting portion may be damaged when handling the passage wall, depending upon locations where the projecting portion is provided which makes up the waterproof construction, it is desirable to avoid such damage.